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Summary of Weighted Average Grant-Date Fair Values And Weighted Average Assumptions Used to Calculate Fair Value of Options Granted (Detail) - Stock Options - $ / shares
3 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Weighted average grant-date fair value $ 96.30 $ 142.51
Valuation assumptions:    
Risk-free interest rate 2.03% 2.93%
Expected option life (years) 4 years 1 month 20 days 4 years 14 days
Expected volatility 42.30% 42.60%